5 tablespoons corn starch mixed with 5 tablespoons milk
4 egg yolks
1 vanilla pod, halved lengthwise
½ cup / 100 grams sugar
1 tablespoon rose water
8 cups / 2 liters vegetable oil
To serve (optional):
Approx. ⅓ cup / 65 grams sugar
2 tablespoons ground cinnamon
Prepare the dough: Using a whisk, mix all the ingredients in a bowl into a sticky uniform dough that borders a thick batter. There is no need to knead this dough. Cover the bowl with cling film and let rise in room temperature for about 1 hour.
Prepare the pastry cream: Place the milk, sugar and vanilla pod in a saucepan and bring to a gentle simmer over medium heat. Remove the vanilla pod, scrape the vanilla seeds into the milk, and return the pod back into the hot milk. Beat the egg yolks and corn starch in a large bowl. Pour a little hot milk into the bowl while whisking continuously (otherwise the yolks will cook). Gradually add the remaining hot milk in a thin stream while whisking continuously. Pour the mixture into the pot, place over medium heat and stir continuously until the mixture thickens to a cream. Remove from the heat, and remove the vanilla pod, and let cool. Stir in the rose water and refrigerate until ready to use.
Frying the sfinj: Heat the oil in a wide deep pot over medium heat. Mix the sugar and cinnamon in a shallow bowl.
Dip your hands in water or grease them with oil. Pull off a tennis ball-sized piece of the soft dough. Using your finger to make a hole in the center of the dough, stretch the hole wide to make a ring and gently slide into the hot oil. Fry until golden brown, about 1½ minutes for each side. Transfer into the sugar cinnamon bowl, evenly coat and transfer to a plate lined with a paper towel. Repeat with the remaining dough.
To serve: Transfer the pastry cream to a piping bag, pipe a dollop in the center of each sfinj and serve. If the pastry cream is too thick, whisk until light and fluffy before transferring to the piping bag.